In this case it's because the compiler would like to link to the standard library (which doesn't exist in this case, this is a kernel). Additionally i need a specific binary file layout, that's what the linker script is for.

in linux, (almost) every executable file (similar to windows .exe file) dynamically links to standard libraries. ("dynamic linking" means it links at run-time, rather than at compile-time). most link at least to a standard library called libc (standard C library).

so when the program starts, before it actually executes any of its program code, the linker program is responsible for hooking up the program to any library that it needs. that's the task of the linker, and that's why technically, each time you start a program, the linker gets called before the program actually starts.

idk why it's in the root directory here.

anyways: try the following: cat /usr/bin/bash | head or replace bash with any other program. you should see something like the following:

where in the first few lines it says /lib64/ld-linux-x86-64.so that's a reference to the linker that should be used.